All the commercially available surveillance systems include a camera with a zoom lens. An operator would usually manually adjust the focal length to obtain clear images for surveillance purpose. Please refer to FIGS. 1 and 2 that are assembled and exploded perspective views, respectively, of a conventional zoom lens 10. As shown, the zoom lens 10 includes a first lens holder 11 and a second lens holder 12. The first lens holder 11 is located at an outer end of the zoom lens 10 and is a focusing lens assembly. The second lens holder 12 is located at an inner end of the zoom lens 10 and is a zoom lens assembly. A surveillance camera may be set to desired surveillant distance and angle of view by adjustably moving the first and the second lens holder 11, 12 forward or rearward.
Three projections 111, 121 are equally spaced along the circumferential surface of the first and the second lens holder 11, 12, respectively. The projections 111, 121 may be screwed to or integrally formed on the first and the second lens holder 11, 12. A barrel of the zoom lens 10 is provided with curved guide grooves 13, 14, corresponding to the projections 111, 121, respectively. When the three projections 111, 121 are moved in the corresponding guide grooves 13, 14, the first and the second lens holder 11, 12 are respectively adjusted in position relative to the zoom lens 10. Moreover, a first and a second focusing ring 15, 16 are respectively mounted to a front and a rear end of the zoom lens 10. The first and the second focusing ring 15, 16 are respectively provided on an inner wall surface with three axially extended linear channels 151, 161 corresponding to the projections 111, 121 on the first and the second lens holder 11, 12. When the first and the second focusing ring 15, 16 are rotated, the channels 151, 161 respectively bring the first and the second lens holder 11, 12 to rotate. When the first and the second lens holder 11, 12 are rotating, the projections 111, 121 thereon are moved along the curved guide grooves 13, 14, respectively, causing the first and the second lens holder 11, 12 to shift forward or rearward. To facilitate easy focus setting, the first and the second focusing ring 15, 16 are provided with a handling lever 152, 162 each, so that the first and the second focusing ring 15, 16 could be conveniently turned.
To set focus for the above-described surveillance camera, it is necessary to open a case or an operating cover of the camera (not shown), so as to expose and move the handling levers 152, 162. Since the handling levers 152, 162 are directly moved with fingers, it is not easy for an operator to move the first and the second lens holder 11, 12 to the most accurate position, bringing confusions to the operator during focus-setting.
It is therefore tried by the inventor to develop a camera lens focus-setting mechanism to allow easy and precise focus-setting using only a driver without the need of open the case or any operating cover of the camera.